1. Field of the Invention
The present invention relates to an image forming apparatus using an electrophotographic system such as a copying machine and a laser beam printer, and more particularly, to an image forming apparatus which transfers a toner image transferred onto an intermediate transfer member to a recording material which is conveyed by a recording material-conveying member.
2. Description of the Related Art
Conventionally, intermediate transfer systems are widely used as an image forming apparatus of an electrophotographic system. According to the intermediate transfer system, a photosensitive drum is electrically charged by an electrically charging device, is exposed to light by an exposure device, and is developed by a developing device. After a toner image on a surface of the photosensitive drum is primarily transferred onto the intermediate transfer member which is opposed to the photosensitive drum, the toner image is secondarily transferred onto a recording material by a recording material-conveying member.
The intermediate transfer system has an issue that color is deviated in the primary transfer, and magnification of an image is varied. Causes thereof are inconsistencies in thickness of the intermediate transfer member, inconsistencies in rotational velocity of the intermediate transfer member caused by eccentricity of a drive roller which rotates the intermediate transfer member, and inconsistencies in rotational velocity of a photosensitive drum caused by eccentricity of the photosensitive drum.
An invention described in Japanese Patent Application Laid-Open No. 2004-287337 relates to a technique in which to suppress an influence of inconsistencies in rotational velocity of an intermediate transfer member, the intermediate transfer member is calibrated, the rotational velocity is detected and the rotational velocity of the intermediate transfer member is controlled to a constant velocity. An invention described in U.S. Pat. No. 6,324,355 relates to a technique in which to suppress an influence of inconsistencies in rotational velocity of an intermediate transfer member, a thickness of the intermediate transfer member is detected and the rotational velocity of the intermediate transfer member is controlled. An invention described in Japanese Patent Application Laid-Open No. 11-249526 relates to a technique in which to suppress an influence of inconsistencies in rotational velocity of an intermediate transfer member, a perimeter of a photosensitive drum and a perimeter of the intermediate transfer member are set to an integral multiple of a perimeter of a drive roller of the intermediate transfer member.
However, when a toner image is secondarily transferred onto a recording material adsorbed on the recording material-conveying member, the recording material-conveying member causes inconsistencies of the rotational velocity by inconsistencies of thickness, a velocity difference is generated between the intermediate transfer member and the recording material-conveying member and the image magnification is prone to be varied at the time of the secondary transfer. The variation in the image magnification caused by the recording material-conveying member cannot be corrected only by detecting the velocity and thickness of the intermediate transfer member and by setting a perimeter of the intermediate transfer member which are the conventional techniques.
The present invention provides an image forming apparatus capable of easily correcting variation in image magnification which is generated when the recording material-conveying member is used.